1. Field
The present disclosure relates to the manufacturing of hydrogenated titanium powders by the metallo-thermic reduction of titanium chlorides, including their hydrogenation, vacuum separation of the subsequently obtained titanium hydride sponge block, followed by crushing and grinding of said block. More specifically, the disclosure is directed towards the cost-cutting, time-saving, and energy-saving manufacture of purified hydrogenated titanium powders, as well as alloying titanium hydride powders, by the improved and combined hydrogen-magnesium reduction of titanium chloride TiCl4, including the vacuum separation (vacuum distillation) of hydrogenated porous titanium compound from magnesium and magnesium chlorides, without the need for any hydro-metallurgical treatment of the produced powders.
The method allows for the manufacturing of titanium and titanium alloy components by low cost powder metallurgy processes, such as the room temperature consolidation of hydrogenated titanium and hydrogenated and alloyed titanium powders, by the die-pressing of near-net shaped articles, or by the direct powder rolling of flat shapes (foils, sheets, plates), or by the cold-isostatic pressing of the “chunky” components, and by other room temperature consolidation processes, followed by sintering. Sintering is performed by the invented special cycle, allowing for the complete and near complete removal of atomic hydrogen from the sintered alloys. Sintered components may be used as-sintered or can be subjected to high temperature post processing by forging, rolling, flow-forming, extrusion and other processing, achieving superior material performance with properties meeting or exceeding the properties of conventional ingot metallurgy of titanium or titanium alloys of identical compositions at considerably reduced manufacturing costs.
2. Description of Related Art
Manufacturing solid titanium articles by powder-metallurgy is becoming more and more popular in today's industry because it can produce near-shape titanium parts without expensive machining and high temperature forming operations. The quality and mechanical properties of commercially-pure titanium or titanium alloy articles manufactured by the room temperature consolidation of the powders and the sintering of green compacts depend upon powder composition, particularly, the content of contaminants such as oxygen, iron, magnesium, chlorine, and other impurities. On the other hand, the cost effectiveness of the powder metallurgy approach depends upon the costs of titanium or titanium hydride powders, which are determined by powder manufacturing steps, especially the costs of reduction and purification operations.
Known processes of manufacturing titanium powders from titanium sponge or sponge-like product include the manufacturing of titanium sponge itself by: (a) magnesium-thermic reduction of titanium chlorides in a reaction retort, (b) preliminary distillation of the reaction mass to the content of magnesium chloride of 5-12%, (c) cooling the obtained titanium sponge block in argon, followed by (d) crushing and grinding the sponge into powder having a particle size of 0-12 mm, (e) preliminary drying of the powder at <250° C., (f) cooling and additional grinding, (g) final distillation of titanium powder from magnesium chloride residues by vacuum separation, (h) hydro-metallurgical treatment, (i) final drying, and (j) final grinding and screening of the titanium powders. Multi-step distillation and hydro-metallurgical treatments make the technology time-consuming, expensive, and economically unproductive.
Numerous disclosures for magnesium-reduction of titanium tetrachloride TiCl4 and the subsequent processing of the obtained titanium sponge are present in the art, starting from U.S. Pat. No. 2,205,854, granted to Wilhelm Kroll in 1940.
Commercial titanium is conventionally produced through Kroll's process which can be written as follows (e.g., for Ti production):
Kroll's Process: TiCl4(gas)+2Mg(liquid)→Ti(sponge,solid)+2MgCl2(liquid)
Most developments have been directed towards improving the quality of the sponge by diminishing the final content of magnesium, chlorine, oxygen, and iron contaminants. Various energy-saving and cost-effective processes in sponge-related technology have been developed during the last two decades; however, solid state processing, like that of powder metallurgy, creates interstitials that degrade the mechanical properties of the produced titanium and titanium alloys and make them unweldable.
Most commercially used titanium powders are produced by a hydride-dehydride (HDH) process, as disclosed in U.S. Pat. No. 6,168,644, by gas atomization, or by the plasma-rotating electrode process, as disclosed in U.S. Pat. No. 6,136,060. Raw materials for the HDH process are either wrought titanium metal, produced by conventional ingot metallurgy processes, or titanium sponge. Both of these raw materials are hydrogenated; then the brittle hydrogenated titanium is ground to the desired powder sizes which are subsequently heated in a vacuum to dehydrogenate them. Essentially, titanium powder production from both titanium wrought alloy and sponge is a multi-step, high-energy, high-cost industrial process. Manufacturing titanium sponge, in particular, is the most expensive part of this technology. Both of these raw materials have their distinctive drawbacks. Titanium powders produced from wrought titanium and titanium alloys are very expensive. Their high production costs come from costly titanium sponge production and very expensive processing costs, that include melting and other high temperature operations. Although titanium sponge is less expensive than the raw material used in HDH powder production, the sponge is always contaminated by impurities such as chlorine, magnesium, sodium, and others. These impurities, an unchangeable trait of HDH-processed sponge, are responsible for inferior fatigue, inferior dynamic properties, and inferior weldability in their alloys.
Other well known drawbacks of titanium powder production from titanium sponge have contributed to the use of the expensive TiC14 reduction and distillation processes. In these processes, the first stage of vacuum separation is carried out at 1020° C., which results in a solid sintered block of the reaction mass and increases the time of sponge distillation. Double-stage vacuum separation, accompanied by multi-stage drying and sponge size reduction increases oxygen content, processing time, and electric energy consumption, and significantly decreases the efficiency of the sponge manufacturing process. When powder is produced from this sponge, multi-stage grinding and hot drying additionally increase the content of gaseous impurities and, in particular, the oxygen content in the obtained powders.
There is a new process described in U.S. Pat. No. 8,007,562 granted to S. Kasparov et al. which discloses the manufacture of pure titanium hydride powder from magnesium-reduced sponge-like hydrogenated porous titanium compound within one production cycle. Any additional hydrometallurgical treatment of the produced powder is excluded, while the exhaust materials of the process such as, magnesium and magnesium chloride, can be readily utilized. This process has made great progress in the quality and productivity of titanium hydride powder, however, it is unhelpful when applied to the manufacture of alloyed titanium powders.
In most of above mentioned sponge manufacturing processes, a periodic removal of magnesium chloride exhaust from the bottom of the retort, as well as reaction interface cooling via argon flow, reduces sponge production time, but there are no gains in either cost-reduction or energy consumption for the overall powder manufacturing process.
The same insignificant result in powder cost reduction is achieved in the process disclosed in JP 61012836, 1986, although some improvement in sponge yield is achieved by the predetermined blowing of TiCl4 at a temperature of <600° C. under argon into molten magnesium. Electric power consumption is decreased by 20% using a condensing vessel in the reactor, promoting the removal of unreacted magnesium and residual magnesium chloride from the reaction zone. This energy saving is associated with sponge production, but does not affect the subsequent powder production process. Powder production requires the further processing of ductile sponge, which needs to be hydrated/dehydrated repetitively with multi-stage processing. The productivity of the magnesium-thermic process is increased by the preliminary cleaning of TiCl4 and its accelerated supply into the reactor. This method also relates only to sponge production and improved sponge quality.
Supplying hot argon through the reaction mass can also speed up the distillation process because it vaporizes the magnesium and magnesium chloride in gaseous form, as disclosed in the U.S. Pat. No. 3,880,652. But the additional expenses associated with heating and supplying high-temperature argon override any production cost savings gained in using it during the distillation stage.
The processes described in U.S. Pat. No. 6,638,336 granted to Drozdenko et al. manufacture titanium powder by (a) magnesium-thermic reduction of titanium chlorides, characterized by the formation of a hollow block of the reaction mass that has an open cavity in the center of the block, (b) thermal-vacuum separation of the hollow block from excessive Mg and MgCl2 at 850-950° C., (c) cooling of the obtained titanium hollow block in a H2-contained atmosphere at an excessive hydrogen pressure, (d) crushing and grinding the hydrogenated titanium block, and (e) hydro-metallurgical treatment of obtained titanium powder in a diluted aqueous solution of at least one chloride selected from magnesium chloride, sodium chloride, potassium chloride, or titanium chloride. The hydro-metallurgical treatment of titanium powder significantly increases labor and processing time, but does not provide a powder of desirable purity, since it contains up to 1% magnesium and chlorine.
The manufacture of high-purity titanium sponge lumps includes crushing the titanium sponge to a particle size of 12-25 mm, followed by its heat-treating at a reduced argon pressure of 600-1100° C. Crushing and heat treatment are repeated several times until the desired purity of the coarse titanium is reached. This method is ineffective for commonly used titanium, and requires HDH processing to obtain powders with the sizes required for industrial applications.
All other known methods of producing titanium, titanium hydride, or alloyed titanium hydride powders from magnesium-reduced sponge or sponge-like porous titanium compound have the same drawbacks: cost and energy savings are realized in only one or two stages of the various manufacturing steps. No known method offers savings throughout the continuous multi-stage processes, and therefore, none of these processes is truly cost-effective.
No one conventional process (except the one described in U.S. Pat. No. 8,007,562) provides a usable and low cost method for manufacturing hydrogenated titanium and/or titanium alloy powder. This is because most of these known processes relate to the manufacturing of sponge lumps which are ductile and need to be treated by the HDH process. In contrast to U.S. Pat. No. 8,007,562, embodiments of the present invention allow for the manufacturing of alloyed titanium hydride powders in one reaction cycle, simultaneously with the reduction of titanium tetrachloride, and improves total productivity and energy saving for the entire process.
No one conventional titanium powder production process can produce low oxygen (below 0.13%) sintered and hot-formed titanium and titanium alloy parts within one production cycle.
Also, none of the processes known from prior art can provide a high productivity titanium powder along with a sufficiently purified hydrogenated titanium powder within just one production cycle. All finished components require additional purification in order to remove impurities, especially magnesium and magnesium chloride, to concentrations required for critical applications and specified in corresponding standards. As a result, the powder metallurgy titanium and titanium alloy components produced from titanium sponge exhibit inferior properties when compared to identical titanium alloys produced through traditional ingot metallurgy. Additionally, the powder metallurgy titanium alloys produced based upon the prior art method are not weldable.